Norcold fridge resistor mod

[markopolo]

Anyone who is interested in the Roadtrek CS Adventurous will probably be aware of the fridge resistor removal suggested by Roadtrek. I try to keep up-to-date on the CS - it's a nice Class B unit.

This would apply to other brands of fridges that use the same electronic unit to control the compressor also.

Here's a PDF data / instruction sheet for the 101N0500 electronic unit:

http://www.secop.com/fileadmin/user_...esi100g102.pdf

Changing the resistor value changes the battery protection setting. The data sheet indicates that the standard battery protection setting is 10.4V cut-out and 11.7V cut-in using an 8.2kΩ resistor.

Removing the resistor entirely changes the battery protection setting to 9.6V cut-out and 10.9V cut-in. The attached pdf file lists the range of resistor values you can choose to increase or decrease the battery protection setting.

Power consumption looks to be limited to 100 watts on the unit. 100w divided by 12v = 8.33 amps.

I'm curious - from a purely technical viewpoint - why the voltage would get down to 10.4v triggering the standard battery protection setting cut-out often enough to make the decision to reduce the battery protection.

Maybe some end user battery care education would help. Running batteries down so low often will reduce the life of the batteries.

I did read about a heater – mullion heater – that prevents condensation (probably between upper & lower door) that draws .5A continuously on the Norcold DE0061. Boondocker's will want to research adding a switch to control that. 0.5A doesn't sound like much but multiply that by 24 hours and it's 12 amps per day.

[stanw909]

Probably the real problem is actually the resistance in the DC wiring to the fridge itself. My Dometic Cool/freeze cf-18 fridge has the battery protection circuit built into it. On my last van I tried plugging it into a cigarette lighter type outlet and it would shutoff when I know the batteries had good charge. I decided to attach them directly to the batteries and got longer run time. See my YouTube review of the Dometic cool/freeze cf-18 for video explanation. So rather than running thicker wire to the fridge, they suggest that you void your fridges warranty(notice they don't do it at factory) to solve their issue.

[stanw909]

BTW. I bought another cool/freeze fridge for my current van and also did a homerun to the battery bank. There is a fuse in the power cable to the fridge. Works great even when batteries get low.

[markopolo]

Good point Stan - it's either the overall system voltage low or, as you mentioned, just the voltage drop on the fridge wire run. Hopefully, there will be some technical discussion on this.

It may end up with a mix of CS units being out there - some with the resistor removed and some where the owner decided to leave the resistor in place. This will be good info for future owners buying used units 5, 10, 15 years etc. down the road.

[booster]

This something that just doesn't make a lot of sense that the modification would even exist, much less ever be needed, unless there was a serious error made in the designing of the power system. The Danfoss compressors work over a big range of voltage inputs, so they certainly must be reducing voltage when above nominal and boosting it when they are below. This would run the current up quite a bit at the low voltages, putting more load on the already taxed system. But I don't think this is the issue.

The more I think about it, the reason they are doing the change may have little or nothing to do with the cut off voltage. It may be they are really trying to address the 11.7 volt cut in setting in the stock configuration.

As far as I know, the Roadtrek "proprietary" secret systems do not have battery monitors on them, so getting low batteries is probably pretty easy if folks think the have lots of battery and have a big inverter, but even if they have a monitor they would have to use it, and actually understand it.

If your batteries are low, say 11.8 volts, and you do a microwave run off the batteries, you could easily trip the 10.4 volt cut out voltage. This, in itself, is not really an issue. The frig just went off, and the food is still cold. If the voltage recovers to 11.7/11.8 volts, the frig comes back on and you are a happy camper. If the voltage doesn't come back that far, you still have lights and things, but the frig stays off, and you have spoiled food and hot beer. No happy camper in that case.

For those of us that live by our obsessing on the battery monitor, this would never be an issue because we wouldn't do a micro run on low batteries without the engine running. But on a B sold to the general population, some sort of cutoff, low battery warning, or such should probably be included, along with instructions of when running high load things isn't appropriate.

Bottom line may just be we are looking at the wrong thing that they are trying to get around. It doesn't really make the modification a good idea, though, as you shouldn't be abusing the batteries like that anyway, but it might save some folks a little food, and beer.

[markopolo]

A DIY under load voltage chart could be helpful to individual owners. I've linked to this before: http://solarjohn.blogspot.ca/2007/03...of-charge.html

It won't be exact but is still way better than having no idea of the state of the batteries in the rig.

I've done the testing twice now with a 60 watt load: http://www.classbforum.com/forums/sh...59&postcount=5

A 100 watt load is easy to do - just plug a 100 watt incandescent bulb into the inverter or a circuit on the inverter.

I might do the test again with a 100 watt load (8.33 amps or so) on the 396 amp hour battery battery bank to create a new under load state of charge chart for my van.

[avanti]

A bit of an aside, but having recently gotten religion and installed a Trimetric battery monitor, I must say that I was insane not to have done it much sooner. Not that hard, not that expensive and incredibly useful. Recommended!

[obgraham]

Keep in mind that in the CS (ETrek style at least), the house batteries are 6 volts, and the proprietary RT system hooks them up into 2 banks of 4 each, then draws 12 volts out of these 2 24 volt systems.
It's likely that the reefer draws from only one of the two banks, and who knows what else is wired into that one. If, for instance the Micro and the Alde and the Instahot were on that same bank, voltage drawdown would be much more likely.
And who's to say that all the CS are wired in the same manner -- RT does indeed change their manufacturing process quite frequently.

[hdevera]

Regarding the CS models, there actually is a low voltage monitor i.e. CO monitor. It will beep when it sees a low voltage. If you have the CS etrek, you should get a battery equalizer (RT has installed it for some owners). I believe this is necessary for all etrek owners. If you don't have one, eventually your batteries will not charge correctly.

Regarding the refrig in this model, I removed the resistor and wired it directly to the batteries with an inline 15 amp fuse. I did this because my refrig never worked correctly on 12v. Once I did this, it has worked fine for a month and is still working well. I believe the wiring to the refrig was just too small and this is what caused the voltage drop to the norcold refrigerator. Also, the Norcold manual states that it should be wired directly to the batteries with certain gauge wires (depending on the distance to the frig) with an inline 15 amp fuse.

[markopolo]

Good to see you here hdevera - I think you were one of the "pioneers" in using an equalizer in an e-trek type unit to help solve issues. It is likely not the perfect fix but it was an improvement. We had a good discussion going here - http://www.classbforum.com/forums/f2...html#post38542 - someday, someone will pick up where that left off. It may not be until all the warranties have expired.

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The best fix for the fridge would seem to be having the appropriate sized wire in place. I know the Battery Protection Settings are optional but changing them by removing the resistor seems to me like treating the symptom rather than solving the root cause of the problem.

I don't know how difficult it would be to upgrade the wire.